The scale on a map is 4cm : 8km. If two cities are 36cm apart on the map, what is the actual distance in km between the two cities?
Answer: The scale means that every 4cm on the map corresponds to an actual distance of 8km. A distance of 36cm on the map is the same as 9 $\cdot$ 4cm. The actual distance between the two cities is 9 $\cdot$ 8km, or 72km.